ゴミ箱がありません
Japanese cities are said to be very tidy. I can definitely confirm this for Kyoto, Nagoya, Tokyo and Hiroshima. It simply seems not to be common amongst Japanese people to throw stuff on the floor as soon as they don't need it any longer.
This is even more astonishing, as there are no trash bins in the streets. Next to some of the ubiquitous drink vending machines you find bins for the empty plastic bottles. They are not for any other trash, however.
If you buy any street food, you can return the paper plate to the vendor. You are supposed to eat the food in front of the stall anyway. Eating while walking around is something one just does not do in Japan. The same goes for trains, except the Shinkansen, where the passengers often eat from their bento boxes.
There seems to be a paradox universal rule about trash cans and tidy streets, which applies to cities both in Japan and Germany. The cleanliness of streets is inversely proportional to the number of garbage cans there.
If you compare Berlin and Munich, you find that to be true. In Berlin there are at least two trash cans at each intersection and the city looks like a junk yard. In Munich you can find one trash can every two blocks, if you are lucky. Still the city is quite tidy.
In case you don't know Japanese, the title of this post is gomibako ga arimasen – there is no trash can.